feat: add CDP connection support for external browsers (#24)

* feat: add CDP connection support for external browsers

Add --cdp flag to connect to browsers via Chrome DevTools Protocol.
This enables control of Electron apps, Chrome instances, or any browser
exposing a CDP endpoint.

- Add cdpPort option to launch command schema
- Implement connectViaCDP() using chromium.connectOverCDP()
- Track browser connection type for proper reconnection handling
- Collect all pages from all contexts for CDP connections

Usage: agent-browser --cdp 9222 snapshot

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* feat: enhance CDP connection handling and improve page tracking

* main.rs update

Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

* fix: verify CDP connection is alive before early return in launch()

Prevents misleading errors when the remote browser crashes by checking
isConnected() before reusing an existing browser reference.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix: reconnect when CDP port changes instead of reusing existing browser

Ensures --cdp flag is respected even when a browser session already exists.
Adds tests for launch() reconnection behavior.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Update src/browser.ts

Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

* fix: improve CDP connection handling and validation

* feat: add CDP connection validation to ensure browser context accessibility

* Update src/browser.ts

Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

* feat: enhance CDP connection handling and add reconnect logic

* fix: improve CDP connection handling during browser closure

* fix: reset cdpPort to null during browser initialization

* feat: enhance browser launch logic to handle CDP connection switching

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

src/protocol.test.ts

@@ -461,6 +461,24 @@ describe('parseCommand', () => {
         expect(result.command.headless).toBe(false);
       }
     });
+
+    it('should parse launch with cdpPort', () => {
+      const result = parseCommand(cmd({ id: '1', action: 'launch', cdpPort: 9222 }));
+      expect(result.success).toBe(true);
+      if (result.success) {
+        expect(result.command.cdpPort).toBe(9222);
+      }
+    });
+
+    it('should reject launch with invalid cdpPort', () => {
+      const result = parseCommand(cmd({ id: '1', action: 'launch', cdpPort: -1 }));
+      expect(result.success).toBe(false);
+    });
+
+    it('should reject launch with non-numeric cdpPort', () => {
+      const result = parseCommand(cmd({ id: '1', action: 'launch', cdpPort: 'invalid' }));
+      expect(result.success).toBe(false);
+    });
   });
 
   describe('mouse actions', () => {